The movie-length episode will be shown at cinemas in Britain and around the world at the same time as it is screened on BBC1 in November

Doctor Who is heading for another dimension – a 3D film to celebrate the sci-fi show’s 50th anniversary.

The movie-length episode will be shown at cinemas in Britain and around the world at the same time as it is screened on BBC1 in November.

A BBC source said: “Filming for the anniversary episode starts in two weeks and there is a real buzz about it, especially because it will be in 3D.

“It is being planned as a TV movie to mark 50 years of the show. It will be the highlight of the celebrations. The episode has been written but we don’t really know yet whether it will be an hour, 75 minutes or 90 minutes.”

Stars of the drama – including Matt Smith who plays the Doctor, and Jenna-Louise Coleman, his sidekick Clara Oswald – received the scripts last week.

And the first hint that it would be a film-length episode came on Friday as Doctor Who actors promoted the new series, which starts on March 30.

Referring to the 50th birthday show, Matt said: “I read the script and I clapped at the end. It’s hilarious, epic and vast. You won’t be disappointed.”

He added: “We are upping the scale of everything. I won’t say anything about the length but there is a bit more for your buck.”

Insiders said the BBC had given Dr Who writer Steven Moffat “free rein” to decide how long it would be – the episodes are usually 45 minutes long. A DVD with behind-the-scenes footage is also being planned.

The anniversary in November will also be marked with a 90-minute BBC2 drama on how the show was created and a fan event at the London Excel.